Tagged: MIT Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 8:56 am on July 4, 2020 Permalink | Reply
    Tags: , , , , MIT, , TESS mission discovers massive ice giant", The exoplanet UCF-1.01, TOI-849 b is the most massive Neptune-sized planet discovered to date and the first to have a density that is comparable to Earth.   

    From MIT News: “TESS mission discovers massive ice giant” 

    MIT News

    From MIT News

    July 1, 2020
    Jennifer Chu

    In our solar system, the “ice giants” Neptune and Uranus are far less dense than rocky Venus and Earth. But astrophysicists on NASA’s TESS mission have now found an exoplanet, TOI-849b, that appears to be 40 times more massive than Earth, yet just as dense. This illustration depicts the exoplanet, UCF-1.01. Like TOI-849b, this exoplanet also orbits close to a star and is like “hot Neptune.” Image credit: NASA/JPL-Caltech.

    NASA/MIT TESS replaced Kepler in search for exoplanets

    The “ice giant” planets Neptune and Uranus are much less dense than rocky, terrestrial planets such as Venus and Earth. Beyond our solar system, many other Neptune-sized planets, orbiting distant stars, appear to be similarly low in density.

    Now, a new planet discovered by NASA’s Transiting Exoplanet Survey Satellite, TESS, seems to buck this trend. The planet, named TOI-849 b, is the 749th “TESS Object of Interest” identified to date. Scientists spotted the planet circling a star about 750 light years away every 18 hours, and estimate it is about 3.5 times larger than Earth, making it a Neptune-sized planet. Surprisingly, this far-flung Neptune appears to be 40 times more massive than Earth and just as dense.

    TOI-849 b is the most massive Neptune-sized planet discovered to date, and the first to have a density that is comparable to Earth.

    “This new planet is more than twice as massive as our own Neptune, which is really unusual,” says Chelsea Huang, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research, and a member of the TESS science team. “Imagine if you had a planet with Earth’s average density, built up to 40 times the Earth’s mass. It’s quite crazy to think what’s happening at the center of a planet with that kind of pressure.”

    The discovery is reported today in the journal Nature. The study’s authors include Huang and members of the TESS science team at MIT.

    A blasted Jupiter?

    Since its launch on April 18, 2018, the TESS satellite has been scanning the skies for planets beyond our solar system. The project is one of NASA’s Astrophysics Explorer missions and is led and operated by MIT. TESS is designed to survey almost the entire sky by pivoting its view every month to focus on a different patch of the sky as it orbits the Earth. As it scans the sky, TESS monitors the light from the brightest, nearest stars, and scientists look for periodic dips in starlight that may signal that a planet is crossing in front of a star.

    Data taken by TESS, in the form of a star’s light curve, or measurements of brightness, is first made available to the TESS science team, an international, multi-institute group of researchers led by scientists at MIT. These researchers get a first look at the data to identify promising planet candidates, or TESS Objects of Interest. These are shared publicly with the general scientific community along with the TESS data for further analysis.

    For the most part, astronomers focus their search for planets on the nearest, brightest stars that TESS has observed. Huang and her team at MIT, however, recently had some extra time to look over data during September and October of 2018, and wondered if anything could be found among the fainter stars. Sure enough, they discovered a significant number of transit-like dips from a star 750 light years away, and soon after, confirmed the existence of TOI-849 b.

    “Stars like this usually don’t get looked at carefully by our team, so this discovery was a happy coincidence,” Huang says.

    Follow-up observations of the faint star with a number of ground-based telescopes further confirmed the planet and also helped to determine its mass and density.

    Huang says that TOI-849 b’s curious proportions are challenging existing theories of planetary formation.

    “We’re really puzzled about how this planet formed,” Huang says. “All the current theories don’t fully explain why it’s so massive at its current location. We don’t expect planets to grow to 40 Earth masses and then just stop there. Instead, it should just keep growing, and end up being a gas giant, like a hot Jupiter, at several hundreds of Earth masses.”

    One hypothesis scientists have come up with to explain the new planet’s mass and density is that perhaps it was once a much larger gas giant, similar to Jupiter and Saturn — planets with more massive envelopes of gas that enshroud cores thought to be as dense as the Earth.

    As the TESS team proposes in the new study, over time, much of the planet’s gassy envelope may have been blasted away by the star’s radiation — not an unlikely scenario, as TOI-849 b orbits extremely close to its host star. Its orbital period is just 0.765 days, or just over 18 hours, which exposes the planet to about 2,000 times the solar radiation that Earth receives from the sun. According to this model, the Neptune-sized planet that TESS discovered may be the remnant core of a much more massive, Jupiter-sized giant.

    “If this scenario is true, TOI-849 b is the only remnant planet core, and the largest gas giant core known to exist,” says Huang. “This is something that gets scientists really excited, because previous theories can’t explain this planet.”

    This research was funded, in part, by NASA.

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    MIT Seal

    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

    MIT Campus

  • richardmitnick 8:09 am on July 1, 2020 Permalink | Reply
    Tags: , , MIT,   

    From MIT News: “Exploring interactions of light and matter” 

    MIT News

    From MIT News

    June 30, 2020
    David L. Chandler

    Juejun Hu pushes the frontiers of optoelectronics for biological imaging, communications, and consumer electronics.

    MIT professor Juejun Hu specializes in optical and photonic devices, whose applications include improving high-speed communications, observing the behavior of molecules, and developing innovations in consumer electronics. Image: Denis Paste

    Growing up in a small town in Fujian province in southern China, Juejun Hu was exposed to engineering from an early age. His father, trained as a mechanical engineer, spent his career working first in that field, then in electrical engineering, and then civil engineering.

    “He gave me early exposure to the field. He brought me books and told me stories of interesting scientists and scientific activities,” Hu recalls. So when it came time to go to college — in China students have to choose their major before enrolling — he picked materials science, figuring that field straddled his interests in science and engineering. He pursued that major at Tsinghua University in Beijing.

    He never regretted that decision. “Indeed, it’s the way to go,” he says. “It was a serendipitous choice.” He continued on to a doctorate in materials science at MIT, and then spent four and a half years as an assistant professor at the University of Delaware before joining the MIT faculty. Last year, Hu earned tenure as an associate professor in MIT’s Department of Materials Science and Engineering.

    In his work at the Institute, he has focused on optical and photonic devices, whose applications include improving high-speed communications, observing the behavior of molecules, designing better medical imaging systems, and developing innovations in consumer electronics such as display screens and sensors.

    “I got fascinated with light,” he says, recalling how he began working in this field. “It has such a direct impact on our lives.”

    Hu is now developing devices to transmit information at very high rates, for data centers or high-performance computers. This includes work on devices called optical diodes or optical isolators, which allow light to pass through only in one direction, and systems for coupling light signals into and out of photonic chips.

    Lately, Hu has been focusing on applying machine-learning methods to improve the performance of optical systems. For example, he has developed an algorithm that improves the sensitivity of a spectrometer, a device for analyzing the chemical composition of materials based on how they emit or absorb different frequencies of light. The new approach made it possible to shrink a device that ordinarily requires bulky and expensive equipment down to the scale of a computer chip, by improving its ability to overcome random noise and provide a clean signal.

    The miniaturized spectrometer makes it possible to analyze the chemical composition of individual molecules with something “small and rugged, to replace devices that are large, delicate, and expensive,” he says.

    Much of his work currently involves the use of metamaterials, which don’t occur in nature and are synthesized usually as a series of ultrathin layers, so thin that they interact with wavelengths of light in novel ways. These could lead to components for biomedical imaging, security surveillance, and sensors on consumer electronics, Hu says. Another project he’s been working on involved developing a kind of optical zoom lens based on metamaterials, which uses no moving parts.

    Hu is also pursuing ways to make photonic and photovoltaic systems that are flexible and stretchable rather than rigid, and to make them lighter and more compact. This could allow for installations in places that would otherwise not be practical. “I’m always looking for new designs to start a new paradigm in optics, [to produce] something that’s smaller, faster, better, and lower cost,” he says.

    Hu says the focus of his research these days is mostly on amorphous materials — whose atoms are randomly arranged as opposed to the orderly lattices of crystal structures — because crystalline materials have been so well-studied and understood. When it comes to amorphous materials, though, “our knowledge is amorphous,” he says. “There are lots of new discoveries in the field.”

    Hu’s wife, Di Chen, whom he met when they were both in China, works in the financial industry. They have twin daughters, Selena and Eos, who are 1 year old, and a son Helius, age 3. Whatever free time he has, Hu says, he likes to spend doing things with his kids.

    Recalling why he was drawn to MIT, he says, “I like this very strong engineering culture.” He especially likes MIT’s strong system of support for bringing new advances out of the lab and into real-world application. “This is what I find really useful.” When new ideas come out of the lab, “I like to see them find real utility,” he adds.

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    MIT Seal

    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

    MIT Campus

  • richardmitnick 12:06 pm on June 12, 2020 Permalink | Reply
    Tags: "Newly observed phenomenon could lead to new quantum devices", A topological Weyl semimetal, , , Kohn anomalies, MIT,   

    From MIT News: “Newly observed phenomenon could lead to new quantum devices” 

    MIT News

    From MIT News

    June 12, 2020
    David L. Chandler

    Exotic states called Kohn anomalies could offer clues to why some materials have the electronic properties they do.

    Diagram depicts the different conditions that give rise to a Kohn anomaly in ordinary metals (at left), versus a material called a Weyl semimetal (at right). The vertical axis shows energy, while the horizontal axis is momentum space. In the conventional metal, a Kohn anomaly can happen when a phonon (q) links two parts of a property called the Fermi surface, which is shown in blue. In the Weyl semimetal, the Kohn anomaly arises when the phonon links two separate Weyl points (kw1-kw2). Image courtesy of the researchers.

    An exotic physical phenomenon known as a Kohn anomaly has been found for the first time in an unexpected type of material by researchers at MIT and elsewhere. They say the finding could provide new insights into certain fundamental processes that help determine why metals and other materials display the complex electronic properties that underlie much of today’s technology.

    The way electrons interact with phonons — which are essentially vibrations passing through a crystalline material — determines the physical processes that take place inside many electronic devices. These interactions affect the way metals resist electric current, the temperature at which some materials suddenly become superconductors, and the very low temperature requirements for quantum computers, among many other processes.

    But electron-phonon interactions have been difficult to study in detail because they are generally very weak. The new study has found a new, stronger kind of unusual electron-phonon interaction: The researchers induced a Kohn anomaly, which was previously thought to exist only in metals, in an exotic material called a topological Weyl semimetal. The finding could help shed light on important aspects of the complex interplay between electrons and phonons, they say.

    The new finding, based on both theoretical predictions and experimental observation, is described this week in the journal Physical Review Letters, in a paper by MIT graduate students Thanh Nguyen and Nina Andrejevic, postdoc Ricardo Pablo-Pedro, Research Scientist Fei Han, Professor Mingda Li, and 14 others at MIT and several other universities and national laboratories.

    Kohn anomalies, first discovered in the 1950s by physicist Walter Kohn, reflect a sudden change, sometimes described as a kind of kink or wiggle, in the graph describing a physical parameter called the electron response function. This discontinuity in an otherwise smooth curve reflects a sudden change of the capability of electrons for shielding phonons. This can give rise to instabilities in the propagation of electrons through the material, and can lead to many new electronic properties.

    These anomalies have been observed before in certain metals and in other highly electrically conductive materials such as graphene, but had never been seen or predicted before in a “topological material,” whose electrical behaviors are robust against perturbation. In this case, a kind of topological material called a Weyl semimetal, specifically tantalum phosphide, was found to be capable of exhibiting this unusual anomaly. Unlike in conventional metals, where a property called the Fermi surface drives the formation of the Kohn anomaly, in this material, the Weyl points serve as the driving force.

    Because electron-phonon couplings are taking place practically everywhere all the time, they can be a major source of disturbance in delicate physical systems such as those used to represent data in quantum computers. Measuring the strength of these interactions, which is key to knowing how to protect such quantum-based technologies, has been very difficult, but this new finding, Li says, provides a way of making such measurements. “The Kohn anomaly can be used to quantify how strong the electron-phonon coupling can be,” he says.

    To measure the interactions, the team made use of advanced neutron and X-ray scattering probes at three national laboratories — Argonne National Laboratory, Oak Ridge National Laboratory, and the National Institute of Standards and Technology — to probe the behavior of the tantalum phosphide material. “We predicted that there is a Kohn anomaly in the material just based on pure theory,” Li explains, Using their calculations, “we could guide the experiments to the point where we want to search for the phenomenon, and we see a very good agreement between theory and the experiments.”

    Martin Greven, a professor of physics at the University of Minnesota who was not involved in this research, says this work “has impressive breadth and depth, spanning both sophisticated theory and scattering experiments. It breaks new ground in condensed matter physics, in that it establishes a new kind of Kohn anomaly.”

    A better understanding of the electron-phonon couplings could help lead the way to developing such materials as better high-temperature superconductors or fault-tolerant quantum computers, the researchers say. This new tool could be used to probe material properties in search of those that remain relatively unaffected at higher temperatures.

    Brent Fultz, a professor of materials science and applied physics at Caltech, who was also not involved in this work, adds that “perhaps these effects will help the development of materials with new thermal or electronic properties, but since they are so new, we need time to think about what they can do.”

    Nguyen, the paper’s lead author, says he thinks this work helps to demonstrate the sometimes overlooked importance of phonons in the behavior of topological materials. Materials such as these, whose surface electrical properties are different from those of the bulk material, are a hot area of current research. “I think this could lead us to further understand processes that would underlie some of these materials that hold a lot of promise for the future,” says Andrejevic, who along with Han was a co-lead author on the paper.

    “Although electron-phonon interaction is long known to exist, the experimental prediction and observation of these interactions is exceedingly rare,” says professor of physics and astronomy Pengcheng Dai at Rice University, who also was not involved in this work. These results, he says, “provide an excellent demonstration of the power of combined theory and experiments as a way to extend our understanding of these exotic materials.”

    The team included researchers at Argonne National Laboratory in Illinois, Oak Ridge National Laboratory in Tennessee, the National Institute of Standards and Technology in Maryland, Pennsylvania State University, and the University of Maryland. The research was supported by the U.S. National Science Foundation, the U.S. Defense Advanced Research Projects Agency, and the U.S. Department of Energy.

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    MIT Seal

    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

    MIT Campus

  • richardmitnick 1:46 pm on June 11, 2020 Permalink | Reply
    Tags: "Engineers put tens of thousands of artificial brain synapses on a single chip", Memristors or memory transistors., MIT, Neuromorphic computing   

    From MIT News: “Engineers put tens of thousands of artificial brain synapses on a single chip” 

    MIT News

    From MIT News

    June 8, 2020
    Jennifer Chu

    A close-up view of a new neuromorphic “brain-on-a-chip” that includes tens of thousands of memristors, or memory transistors. Credit: Peng Lin

    A new MIT-fabricated “brain-on-a-chip” reprocessed an image of MIT’s Killian Court, including sharpening and blurring the image, more reliably than existing neuromorphic designs. Image courtesy of the researchers.

    The new chip (top left) is patterned with tens of thousands of artificial synapses, or “memristors,” made with a silver-copper alloy. When each memristor is stimulated with a specific voltage corresponding to a pixel and shade in a gray-scale image (in this case, a Captain America shield), the new chip reproduced the same crisp image, more reliably than chips fabricated with memristors of different materials. Image courtesy of the researchers.

    The design could advance the development of small, portable AI devices.

    MIT engineers have designed a “brain-on-a-chip,” smaller than a piece of confetti, that is made from tens of thousands of artificial brain synapses known as memristors — silicon-based components that mimic the information-transmitting synapses in the human brain.

    The researchers borrowed from principles of metallurgy to fabricate each memristor from alloys of silver and copper, along with silicon. When they ran the chip through several visual tasks, the chip was able to “remember” stored images and reproduce them many times over, in versions that were crisper and cleaner compared with existing memristor designs made with unalloyed elements.

    Their results, published today in the journal Nature Nanotechnology, demonstrate a promising new memristor design for neuromorphic devices — electronics that are based on a new type of circuit that processes information in a way that mimics the brain’s neural architecture. Such brain-inspired circuits could be built into small, portable devices, and would carry out complex computational tasks that only today’s supercomputers can handle.

    “So far, artificial synapse networks exist as software. We’re trying to build real neural network hardware for portable artificial intelligence systems,” says Jeehwan Kim, associate professor of mechanical engineering at MIT. “Imagine connecting a neuromorphic device to a camera on your car, and having it recognize lights and objects and make a decision immediately, without having to connect to the internet. We hope to use energy-efficient memristors to do those tasks on-site, in real-time.”

    Wandering ions

    Memristors, or memory transistors, are an essential element in neuromorphic computing. In a neuromorphic device, a memristor would serve as the transistor in a circuit, though its workings would more closely resemble a brain synapse — the junction between two neurons. The synapse receives signals from one neuron, in the form of ions, and sends a corresponding signal to the next neuron.

    A transistor in a conventional circuit transmits information by switching between one of only two values, 0 and 1, and doing so only when the signal it receives, in the form of an electric current, is of a particular strength. In contrast, a memristor would work along a gradient, much like a synapse in the brain. The signal it produces would vary depending on the strength of the signal that it receives. This would enable a single memristor to have many values, and therefore carry out a far wider range of operations than binary transistors.

    Like a brain synapse, a memristor would also be able to “remember” the value associated with a given current strength, and produce the exact same signal the next time it receives a similar current. This could ensure that the answer to a complex equation, or the visual classification of an object, is reliable — a feat that normally involves multiple transistors and capacitors.

    Ultimately, scientists envision that memristors would require far less chip real estate than conventional transistors, enabling powerful, portable computing devices that do not rely on supercomputers, or even connections to the Internet.

    Existing memristor designs, however, are limited in their performance. A single memristor is made of a positive and negative electrode, separated by a “switching medium,” or space between the electrodes. When a voltage is applied to one electrode, ions from that electrode flow through the medium, forming a “conduction channel” to the other electrode. The received ions make up the electrical signal that the memristor transmits through the circuit. The size of the ion channel (and the signal that the memristor ultimately produces) should be proportional to the strength of the stimulating voltage.

    Kim says that existing memristor designs work pretty well in cases where voltage stimulates a large conduction channel, or a heavy flow of ions from one electrode to the other. But these designs are less reliable when memristors need to generate subtler signals, via thinner conduction channels.

    The thinner a conduction channel, and the lighter the flow of ions from one electrode to the other, the harder it is for individual ions to stay together. Instead, they tend to wander from the group, disbanding within the medium. As a result, it’s difficult for the receiving electrode to reliably capture the same number of ions, and therefore transmit the same signal, when stimulated with a certain low range of current.

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    MIT Seal

    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

    MIT Campus

  • richardmitnick 10:20 am on June 8, 2020 Permalink | Reply
    Tags: "Transparent graphene electrodes might lead to new generation of solar cells", , Civil and environmental engineering, Electrical Engineering and computer science, MIT, , ,   

    From MIT News: “Transparent graphene electrodes might lead to new generation of solar cells” 

    MIT News

    From MIT News

    June 5, 2020
    David L. Chandler

    New roll-to-roll production method could enable lightweight, flexible solar devices and a new generation of display screens.

    A new manufacturing process for graphene is based on using an intermediate carrier layer of material after the graphene is laid down through a vapor deposition process. The carrier allows the ultrathin graphene sheet, less than a nanometer (billionth of a meter) thick, to be easily lifted off from a substrate, allowing for rapid roll-to-roll manufacturing. These figures show this process for making graphene sheets, along with a photo of the proof-of-concept device used (b). Courtesy of the researchers.

    A new way of making large sheets of high-quality, atomically thin graphene could lead to ultra-lightweight, flexible solar cells, and to new classes of light-emitting devices and other thin-film electronics.

    The new manufacturing process, which was developed at MIT and should be relatively easy to scale up for industrial production, involves an intermediate “buffer” layer of material that is key to the technique’s success. The buffer allows the ultrathin graphene sheet, less than a nanometer (billionth of a meter) thick, to be easily lifted off from its substrate, allowing for rapid roll-to-roll manufacturing.

    The process is detailed in a paper published yesterday in Advanced Functional Materials, by MIT postdocs Giovanni Azzellino and Mahdi Tavakoli; professors Jing Kong, Tomas Palacios, and Markus Buehler; and five others at MIT.

    Finding a way to make thin, large-area, transparent electrodes that are stable in open air has been a major quest in thin-film electronics in recent years, for a variety of applications in optoelectronic devices — things that either emit light, like computer and smartphone screens, or harvest it, like solar cells. Today’s standard for such applications is indium tin oxide (ITO), a material based on rare and expensive chemical elements.

    Many research groups have worked on finding a replacement for ITO, focusing on both organic and inorganic candidate materials. Graphene, a form of pure carbon whose atoms are arranged in a flat hexagonal array, has extremely good electrical and mechanical properties, yet it is vanishingly thin, physically flexible, and made from an abundant, inexpensive material. Furthermore, it can be easily grown in the form of large sheets by chemical vapor deposition (CVD), using copper as a seed layer, as Kong’s group has demonstrated. However, for device applications, the trickiest part has been finding ways to release the CVD-grown graphene from its native copper substrate.

    This release, known as graphene transfer process, tends to result in a web of tears, wrinkles, and defects in the sheets, which disrupts the film continuity and therefore drastically reduces their electrical conductivity. But with the new technology, Azzellino says, “now we are able to reliably manufacture large-area graphene sheets, transfer them onto whatever substrate we want, and the way we transfer them does not affect the electrical and mechanical properties of the pristine graphene.”

    The key is the buffer layer, made of a polymer material called parylene, that conforms at the atomic level to the graphene sheets on which it is deployed. Like graphene, parylene is produced by CVD, which simplifies the manufacturing process and scalability.

    As a demonstration of this technology, the team made proof-of-concept solar cells, adopting a thin-film polymeric solar cell material, along with the newly formed graphene layer for one of the cell’s two electrodes, and a parylene layer that also serves as a device substrate. They measured an optical transmittance close to 90 percent for the graphene film under visible light.

    The prototyped graphene-based solar cell improves by roughly 36 times the delivered power per weight, compared to ITO-based state-of-the-art devices. It also uses 1/200 the amount of material per unit area for the transparent electrode. And, there is a further fundamental advantage compared to ITO: “Graphene comes for almost free,” Azzellino says.

    “Ultra-lightweight graphene-based devices can pave the way to a new generation of applications,” he says. “So if you think about portable devices, the power per weight becomes a very important figure of merit. What if we could deploy a transparent solar cell on your tablet that is able to power up the tablet itself?” Though some further development would be needed, such applications should ultimately be feasible with this new method, he says.

    The buffer material, parylene, is widely used in the microelectronics industry, usually to encapsulate and protect electronic devices. So the supply chains and equipment for using the material already are widespread, Azzellino says. Of the three existing types of parylene, the team’s tests showed that one of them, which contains more chlorine atoms, was by far the most effective for this application.

    The atomic proximity of chlorine-rich parylene to the underlying graphene as the layers are sandwiched together provides a further advantage, by offering a kind of “doping” for graphene, finally providing a more reliable and nondestructive approach for conductivity improvement of large-area graphene, unlike many others that have been tested and reported so far.

    “The graphene and the parylene films are always face-to-face,” Azzellino says. “So basically, the doping action is always there, and therefore the advantage is permanent.”

    The research team also included Marek Hempel, Ang-Yu Lu, Francisco Martin-Martinez, Jiayuan Zhao and Jingjie Yeo, all at MIT. The work was supported by Eni SpA through the MIT Energy Initiative, the U.S. Army Research Office through the Institute for Soldier Nanotechnologies, and the Office of Naval Research.

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    MIT Seal

    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

    MIT Campus

  • richardmitnick 10:12 am on June 5, 2020 Permalink | Reply
    Tags: "Giving soft robots feeling", , GelFlex, Magic ball senses, MIT, Paper: "Exoskeleton-covered soft finger with vision-based proprioception and exteroception", Paper: "Exoskeleton-covered soft finger with vision-based proprioception andexteroception"   

    From MIT News: “Giving soft robots feeling” 

    MIT News

    From MIT News

    June 1, 2020
    Rachel Gordon | MIT CSAIL

    One of the hottest topics in robotics is the field of soft robots, which utilizes squishy and flexible materials rather than traditional rigid materials. But soft robots have been limited due to their lack of good sensing. A good robotic gripper needs to feel what it is touching (tactile sensing), and it needs to sense the positions of its fingers (proprioception). Such sensing has been missing from most soft robots.

    In a new pair of papers, researchers from MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) came up with new tools to let robots better perceive what they’re interacting with: the ability to see and classify items, and a softer, delicate touch.

    “We wish to enable seeing the world by feeling the world. Soft robot hands have sensorized skins that allow them to pick up a range of objects, from delicate, such as potato chips, to heavy, such as milk bottles,” says CSAIL Director Daniela Rus, the Andrew and Erna Viterbi Professor of Electrical Engineering and Computer Science and the deputy dean of research for the MIT Stephen A. Schwarzman College of Computing.

    One paper “Exoskeleton-covered soft finger with vision-based proprioception and exteroception” [ https://arxiv.org/abs/1910.01287 ] builds off last year’s research from MIT and Harvard University, where a team developed a soft and strong robotic gripper in the form of a cone-shaped origami structure. It collapses in on objects much like a Venus’ flytrap, to pick up items that are as much as 100 times its weight.

    To get that newfound versatility and adaptability even closer to that of a human hand, a new team came up with a sensible addition: tactile sensors, made from latex “bladders” (balloons) connected to pressure transducers. The new sensors let the gripper not only pick up objects as delicate as potato chips, but it also classifies them — letting the robot better understand what it’s picking up, while also exhibiting that light touch.

    When classifying objects, the sensors correctly identified 10 objects with over 90 percent accuracy, even when an object slipped out of grip.

    “Unlike many other soft tactile sensors, ours can be rapidly fabricated, retrofitted into grippers, and show sensitivity and reliability,” says MIT postdoc Josie Hughes, the lead author on a new paper about the sensors. “We hope they provide a new method of soft sensing that can be applied to a wide range of different applications in manufacturing settings, like packing and lifting.”

    In a second paper “Exoskeleton-covered soft finger with vision-based proprioception andexteroception” [ https://arxiv.org/pdf/1910.01287.pdf ], a group of researchers created a soft robotic finger called “GelFlex” that uses embedded cameras and deep learning to enable high-resolution tactile sensing and “proprioception” (awareness of positions and movements of the body).

    The gripper, which looks much like a two-finger cup gripper you might see at a soda station, uses a tendon-driven mechanism to actuate the fingers. When tested on metal objects of various shapes, the system had over 96 percent recognition accuracy.

    “Our soft finger can provide high accuracy on proprioception and accurately predict grasped objects, and also withstand considerable impact without harming the interacted environment and itself,” says Yu She, lead author on a new paper on GelFlex. “By constraining soft fingers with a flexible exoskeleton, and performing high-resolution sensing with embedded cameras, we open up a large range of capabilities for soft manipulators.”

    Magic ball senses

    The magic ball gripper is made from a soft origami structure, encased by a soft balloon. When a vacuum is applied to the balloon, the origami structure closes around the object, and the gripper deforms to its structure.

    While this motion lets the gripper grasp a much wider range of objects than ever before, such as soup cans, hammers, wine glasses, drones, and even a single broccoli floret, the greater intricacies of delicacy and understanding were still out of reach — until they added the sensors.

    When the sensors experience force or strain, the internal pressure changes, and the team can measure this change in pressure to identify when it will feel that again.

    In addition to the latex sensor, the team also developed an algorithm which uses feedback to let the gripper possess a human-like duality of being both strong and precise — and 80 percent of the tested objects were successfully grasped without damage.

    The team tested the gripper-sensors on a variety of household items, ranging from heavy bottles to small, delicate objects, including cans, apples, a toothbrush, a water bottle, and a bag of cookies.

    Going forward, the team hopes to make the methodology scalable, using computational design and reconstruction methods to improve the resolution and coverage using this new sensor technology. Eventually, they imagine using the new sensors to create a fluidic sensing skin that shows scalability and sensitivity.

    Hughes co-wrote the new paper with Rus, which they will present virtually at the 2020 International Conference on Robotics and Automation.


    In the second paper, a CSAIL team looked at giving a soft robotic gripper more nuanced, human-like senses. Soft fingers allow a wide range of deformations, but to be used in a controlled way there must be rich tactile and proprioceptive sensing. The team used embedded cameras with wide-angle “fisheye” lenses that capture the finger’s deformations in great detail.

    To create GelFlex, the team used silicone material to fabricate the soft and transparent finger, and put one camera near the fingertip and the other in the middle of the finger. Then, they painted reflective ink on the front and side surface of the finger, and added LED lights on the back. This allows the internal fish-eye camera to observe the status of the front and side surface of the finger.

    The team trained neural networks to extract key information from the internal cameras for feedback. One neural net was trained to predict the bending angle of GelFlex, and the other was trained to estimate the shape and size of the objects being grabbed. The gripper could then pick up a variety of items such as a Rubik’s cube, a DVD case, or a block of aluminum.

    During testing, the average positional error while gripping was less than 0.77 millimeter, which is better than that of a human finger. In a second set of tests, the gripper was challenged with grasping and recognizing cylinders and boxes of various sizes. Out of 80 trials, only three were classified incorrectly.

    In the future, the team hopes to improve the proprioception and tactile sensing algorithms, and utilize vision-based sensors to estimate more complex finger configurations, such as twisting or lateral bending, which are challenging for common sensors, but should be attainable with embedded cameras.

    Yu She co-wrote the GelFlex paper with MIT graduate student Sandra Q. Liu, Peiyu Yu of Tsinghua University, and MIT Professor Edward Adelson. They will present the paper virtually at the 2020 International Conference on Robotics and Automation.

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    MIT Seal

    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

    MIT Campus

  • richardmitnick 9:52 am on June 5, 2020 Permalink | Reply
    Tags: "Carbon nanotube transistors (CNFETs) make the leap from lab to factory floor", CNFETs can be manufactured at near-room temperatures., MIT, Technique paves the way for more energy efficient 3D microprocessors.   

    From MIT News: “Carbon nanotube transistors make the leap from lab to factory floor” 

    MIT News

    From MIT News

    June 1, 2020
    Becky Ham

    MIT researchers demonstrated a method to manufacture carbon nanotube transistors in commercial facilities that fabricate silicon-based transistors. This photograph shows Anthony Ratkovich, left, and Mindy D. Bishop, who is holding an example of a silicon wafer. Courtesy of the researchers.

    Technique paves the way for more energy efficient, 3D microprocessors.

    Carbon nanotube transistors are a step closer to commercial reality, now that MIT researchers have demonstrated that the devices can be made swiftly in commercial facilities, with the same equipment used to manufacture the silicon-based transistors that are the backbone of today’s computing industry.

    Carbon nanotube field-effect transistors or CNFETs are more energy-efficient than silicon field-effect transistors and could be used to build new types of three-dimensional microprocessors. But until now, they’ve existed mostly in an “artisanal” space, crafted in small quantities in academic laboratories.

    In a study published June 1 in Nature Electronics, however, scientists show how CNFETs can be fabricated in large quantities on 200-millimeter wafers that are the industry standard in computer chip design. The CNFETs were created in a commercial silicon manufacturing facility and a semiconductor foundry in the United States.

    After analyzing the deposition technique used to make the CNFETs, Max Shulaker, an MIT assistant professor of electrical engineering and computer science, and his colleagues made some changes to speed up the fabrication process by more than 1,100 times compared to the conventional method, while also reducing the cost of production. The technique deposited carbon nanotubes edge to edge on the wafers, with 14,400 by 14,400 arrays CFNETs distributed across multiple wafers.

    Shulaker, who has been designing CNFETs since his PhD days, says the new study represents “a giant step forward, to make that leap into production-level facilities.”

    Bridging the gap between lab and industry is something that researchers “don’t often get a chance to do,” he adds. “But it’s an important litmus test for emerging technologies.”

    Other MIT researchers on the study include lead author Mindy D. Bishop, a PhD student in the Harvard-MIT Health Sciences and Technology program, along with Gage Hills, Tathagata Srimani, and Christian Lau.

    Solving the spaghetti problem

    For decades, improvements in silicon-based transistor manufacturing have brought down prices and increased energy efficiency in computing. That trend may be nearing its end, however, as increasing numbers of transistors packed into integrated circuits do not appear to be increasing energy efficiency at historic rates.

    CNFETs are an attractive alternative technology because they are “around an order of magnitude more energy efficient” than silicon-based transistors, says Shulaker.

    Unlike silicon-based transistors, which are made at temperatures around 450 to 500 degrees Celsius, CNFETs also can be manufactured at near-room temperatures. “This means that you can actually build layers of circuits right on top of previously fabricated layers of circuits, to create a three-dimensional chip,” Shulaker explains. “You can’t do this with silicon-based technology, because you would melt the layers underneath.”

    A 3D computer chip, which might combine logic and memory functions, is projected to “beat the performance of a state-of-the-art 2D chip made from silicon by orders of magnitude,” he says.

    One of the most effective ways to build CFNETs in the lab is a method for depositing nanotubes called incubation, where a wafer is submerged in a bath of nanotubes until the nanotubes stick to the wafer’s surface.

    The performance of the CNFET is dictated in large part by the deposition process, says Bishop, which affects both the number of carbon nanotubes on the surface of the wafer and their orientation. They’re “either stuck onto the wafer in random orientations like cooked spaghetti or all aligned in the same direction like uncooked spaghetti still in the package,” she says.

    Aligning the nanotubes perfectly in a CNFET leads to ideal performance, but alignment is difficult to obtain. “It’s really hard to lay down billions of tiny 1-nanometer diameter nanotubes in a perfect orientation across a large 200-millimeter wafer,” Bishop explains. “To put these length scales into context, it’s like trying to cover the entire state of New Hampshire in perfectly oriented dry spaghetti.”

    The incubation method, while practical for industry, doesn’t align the nanotubes at all. They end up on the wafer more like cooked spaghetti, which the researchers initially didn’t think would deliver sufficiently high CNFET performance, Bishop says. After their experiments, however, she and her colleagues concluded that the simple incubation process would work to produce a CNFET that could outperform a silicon-based transistor.

    CNFETs beyond the beaker

    Careful observations of the incubation process showed the researchers how to alter the process to make it more viable for industrial production. For instance, they found that dry cycling, a method of intermittently drying out the submerged wafer, could dramatically reduce the incubation time — from 48 hours to 150 seconds.

    Another new method called ACE (artificial concentration through evaporation) deposited small amounts of nanotube solution on a wafer instead of submerging the wafer in a tank. The slow evaporation of the solution increased the concentration of carbon nanotubes and the overall density of nanotubes deposited on the wafer.

    These changes were necessary before the process could be tried on an industrial scale, Bishop says: “In our lab, we’re fine to let a wafer sit for a week in a beaker, but for a company, they don’t have that luxury.”

    The “elegantly simple tests” that helped them understand and improve on the incubation method, she says, “proved really important for addressing concerns that maybe academics don’t have, but certainly industry has, when they look at setting up a new process.”

    The researchers worked with Analog Devices, a commercial silicon manufacturing facility, and SkyWater Technology, a semiconductor foundry, to fabricate CNFETs using the improved method. They were able to use the same equipment that the two facilities use to make silicon-based wafers, while also ensuring that the nanotube solutions met the strict chemical and contaminant requirements of the facilities.

    “We were extremely lucky to work closely with our industry collaborators and learn about their requirements and iterate our development with their input,” says Bishop, who noted that the partnership helped them develop an automated, high-volume and low-cost process.

    The two facilities showed a “serious commitment to research and development and exploring the edge” of emerging technologies, Shulaker adds.

    “We are excited to continue our work building out the critical infrastructure for enabling commercial market availability of CNFETs. This effort is a pivotal move to bring back manufacturing of leading-edge advanced computing to the U.S.,” said Thomas Sonderman, president of SkyWater.

    The next steps, already underway, will be to build different types of integrated circuits out of CNFETs in an industrial setting and explore some of the new functions that a 3D chip could offer, he says. “The next goal is for this to transition from being academically interesting to something that will be used by folks, and I think this is a very important step in this direction.”

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    MIT Seal

    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

    MIT Campus

  • richardmitnick 10:16 am on May 18, 2020 Permalink | Reply
    Tags: "Melting glaciers cool the Southern Ocean", , MIT   

    From MIT News: “Melting glaciers cool the Southern Ocean” 

    MIT News

    From MIT News

    May 17, 2020
    Fernanda Ferreira | School of Science

    MIT scientists suggest sea ice extent in the Southern Ocean may increase with glacial melting in Antarctica. This image shows a view of the Earth on Sept. 21, 2005 with the full Antarctic region visible. Photo: NASA/Goddard Space Flight Center.

    Discrepancies between observed and modeled surface temperatures (shown in Celsius) in the Southern Ocean might be explained by glacial melt. Image courtesy of the researchers.

    Research suggests glacial melting might explain the recent decadal cooling and sea ice expansion across Antarctica’s Southern Ocean.

    Tucked away at the very bottom of the globe surrounding Antarctica, the Southern Ocean has never been easy to study. Its challenging conditions have placed it out of reach to all but the most intrepid explorers. For climate modelers, however, the surface waters of the Southern Ocean provide a different kind of challenge: It doesn’t behave the way they predict it would. “It is colder and fresher than the models expected,” says Craig Rye, a postdoc in the group of Cecil and Ida Green Professor of Oceanography John Marshall within MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS).

    In recent decades, as the world warms, the Southern Ocean’s surface temperature has cooled, allowing the amount of ice that crystallizes on the surface each winter to grow. This is not what climate models anticipated, and a recent study accepted in Geophysical Research Letters attempts to disentangle that discrepancy. “This paper is motivated by a disagreement between what should be happening according to simulations and what we observe,” says Rye, the lead author of the paper who is currently working remotely from NASA’s Goddard Institute for Space Studies, or GISS, in New York City.

    “This is a big conundrum in the climate community,” says Marshall, a co-author on the paper along with Maxwell Kelley, Gary Russell, Gavin A. Schmidt, and Larissa S. Nazarenko of GISS; James Hansen of Columbia University’s Earth Institute; and Yavor Kostov of the University of Exeter. There are 30 or so climate models used to foresee what the world might look like as the climate changes. According to Marshall, models don’t match the recent observations of surface temperature in the Southern Ocean, leaving scientists with a question that Rye, Marshall, and their colleagues intend to answer: how can the Southern Ocean cool when the rest of the Earth is warming?

    This isn’t the first time Marshall has investigated the Southern Ocean and its climate trends. In 2016, Marshall and Yavor Kostov PhD ’16 published a paper exploring two possible influences driving the observed ocean trends: greenhouse gas emissions, and westerly winds — strengthened by expansion of the Antarctic ozone hole — blowing cold water northward from the continent. Both explained some of the cooling in the Southern Ocean, but not all of it. “We ended that paper saying there must be something else,” says Marshall.

    That something else could be meltwater released from thawing glaciers. Rye has probed the influence of glacial melt in the Southern Ocean before, looking at its effect on sea surface height during his PhD at the University of Southampton in the UK. “Since then, I’ve been interested in the potential for glacial melt playing a role in Southern Ocean climate trends,” says Rye.

    The group’s recent paper uses a series of “perturbation” experiments carried out with the GISS global climate model where they abruptly introduce a fixed increase in melt water around Antarctica and then record how the model responds. The researchers then apply the model’s response to a previous climate state to estimate how the climate should react to the observed forcing. The results are then compared to the observational record, to see if a factor is missing. This method is called hindcasting.

    Marshall likens perturbation experiments to walking into a room and being confronted with an object you don’t recognize. “You might give it a gentle whack to see what it’s made of,” says Marshall. Perturbation experiments, he explains, are like whacking the model with inputs, such as glacial melt, greenhouse gas emissions, and wind, to uncover the relative importance of these factors on observed climate trends.

    In their hindcasting, they estimate what would have happened to a pre-industrial Southern Ocean (before anthropogenic climate change) if up to 750 gigatons of meltwater were added each year. That quantity of 750 gigatons of meltwater is estimated from observations of both floating ice shelves and the ice sheet that lies over land above sea level. A single gigaton of water is very large — it can fill 400,000 Olympic swimming pools, meaning 750 gigatons of meltwater is equivalent to pouring water from 300 million Olympic swimming pools into the ocean every year.

    When this increase in glacial melt was added to the model, it led to sea surface cooling, decreases in salinity, and expansion of sea ice coverage that are consistent with observed trends in the Southern Ocean during the last few decades. Their model results suggest that meltwater may account for the majority of previously misunderstood Southern Ocean cooling.

    The model shows that a warming climate may be driving, in a counterintuitive way, more sea ice by increasing the rate of melting of Antarctica’s glaciers. According to Marshall, the paper may solve the disconnect between what was expected and what was observed in the Southern Ocean, and answers the conundrum he and Kostov pointed to in 2016. “The missing process could be glacial melt.”

    Research like Rye’s and Marshall’s help project the future state of Earth’s climate and guide society’s decisions on how to prepare for that future. By hindcasting the Southern Ocean’s climate trends, they and their colleagues have identified another process, which must be incorporated into climate models. “What we’ve tried to do is ground this model in the historical record,” says Marshall. Now the group can probe the GISS model response with further “what if?” glacial melt scenarios to explore what might be in store for the Southern Ocean

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    MIT Seal

    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

    MIT Campus

  • richardmitnick 10:19 am on May 11, 2020 Permalink | Reply
    Tags: "Researchers map tiny twists in “magic-angle” graphene", , MIT,   

    From MIT News: “Researchers map tiny twists in “magic-angle” graphene” 

    MIT News

    From MIT News

    May 7, 2020
    Jennifer Chu

    In this illustration, two sheets of graphene are stacked together at a slightly offset “magic” angle, which can become either an insulator or superconductor. “We placed one sheet of graphene on top of another, similar to placing plastic wrap on top of plastic wrap,” MIT professor Pablo Jarillo-Herrero says. “You would expect there would be wrinkles, and regions where the two sheets would be a bit twisted, some less twisted, just as we see in graphene.” Image: José-Luis Olivares, MIT.

    Results could help designers engineer high-temperature superconductors and quantum computing devices.

    Made of a single layer of carbon atoms linked in a hexagonal honeycomb pattern, graphene’s structure is simple and seemingly delicate. Since its discovery in 2004, scientists have found that graphene is in fact exceptionally strong. And although graphene is not a metal, it conducts electricity at ultrahigh speeds, better than most metals.

    In 2018, MIT scientists led by Pablo Jarillo-Herrero and Yuan Cao discovered that when two sheets of graphene are stacked together at a slightly offset “magic” angle, the new “twisted” graphene structure can become either an insulator, completely blocking electricity from flowing through the material, or paradoxically, a superconductor, able to let electrons fly through without resistance. It was a monumental discovery that helped launch a new field known as “twistronics,” the study of electronic behavior in twisted graphene and other materials.

    Now the MIT team reports their latest advancements in graphene twistronics, in two papers published this week in the journal Nature: “Tunable correlated states and spin-polarized phases in twisted bilayer–bilayer graphene” and “Mapping the twist-angle disorder and Landau levels in magic-angle graphene“.

    In the first study, the researchers, along with collaborators at the Weizmann Institute of Science, have imaged and mapped an entire twisted graphene structure for the first time, at a resolution fine enough that they are able to see very slight variations in local twist angle across the entire structure.

    The results revealed regions within the structure where the angle between the graphene layers veered slightly away from the average offset of 1.1 degrees.

    The team detected these variations at an ultrahigh angular resolution of 0.002 degree. That’s equivalent to being able to see the angle of an apple against the horizon from a mile away.

    They found that structures with a narrower range of angle variations had more pronounced exotic properties, such as insulation and superconductivity, versus structures with a wider range of twist angles.

    “This is the first time an entire device has been mapped out to see what is the twist angle at a given region in the device,” says Jarillo-Herrero, the Cecil and Ida Green Professor of Physics at MIT. “And we see that you can have a little bit of variation and still show superconductivity and other exotic physics, but it can’t be too much. We now have characterized how much twist variation you can have, and what is the degradation effect of having too much.”

    In the second study, the team report creating a new twisted graphene structure with not two, but four layers of graphene. They observed that the new four-layer magic-angle structure is more sensitive to certain electric and magnetic fields compared to its two-layer predecessor. This suggests that researchers may be able to more easily and controllably study the exotic properties of magic-angle graphene in four-layer systems.

    “These two studies are aiming to better understand the puzzling physical behavior of magic-angle twistronics devices,” says Cao, a graduate student at MIT. “Once understood, physicists believe these devices could help design and engineer a new generation of high-temperature superconductors, topological devices for quantum information processing, and low-energy technologies.”

    Like wrinkles in plastic wrap

    Since Jarillo-Herrero and his group first discovered magic-angle graphene, others have jumped at the chance to observe and measure its properties. Several groups have imaged magic-angle structures, using scanning tunneling microscopy, or STM, a technique that scans a surface at the atomic level. However, researchers have only been able to scan small patches of magic-angle graphene, spanning at most a few hundred square nanometers, using this approach.

    “Going over an entire micron-scale structure to look at millions of atoms is something that STM is not best suited for,” Jarillo-Herrero says. “In principle it could be done, but would take an enormous amount of time.”

    So the group consulted with researchers at the Weizmann Institute for Science, who had developed a scanning technique they call “scanning nano-SQUID,” where SQUID stands for Superconducting Quantum Interference Device. Conventional SQUIDs resemble a small bisected ring, the two halves of which are made of superconducting material and joined together by two junctions. Fit around the tip of a device similar to an STM, a SQUID can measure a sample’s magnetic field flowing through the ring at a microscopic scale. The Weizmann Institute researchers scaled down the SQUID design to sense magnetic fields at the nanoscale.

    When magic-angle graphene is placed in a small magnetic field, it generates persistent currents across the structure, due to the formation of what are known as “Landau levels.” These Landau levels, and hence the persistent currents, are very sensitive to the local twist angle, for instance, resulting in a magnetic field with a different magnitude, depending on the precise value of the local twist angle. In this way, the nano-SQUID technique can detect regions with tiny offsets from 1.1 degrees.

    “It turned out to be an amazing technique that can pick up miniscule angle variations of 0.002 degrees away from 1.1 degrees,” Jarillo-Herrero says. “This was very good for mapping magic-angle graphene.”

    The group used the technique to map two magic-angle structures: one with a narrow range of twist variations, and another with a broader range.

    “We placed one sheet of graphene on top of another, similar to placing plastic wrap on top of plastic wrap,” Jarillo-Herrero says. “You would expect there would be wrinkles, and regions where the two sheets would be a bit twisted, some less twisted, just as we see in graphene.”

    They found that the structure with a narrower range of twist variations had more pronounced properties of exotic physics, such as superconductivity, compared with the structure with more twist variations.

    “Now that we can directly see these local twist variations, it might be interesting to study how to engineer variations in twist angles to achieve different quantum phases in a device,” Cao says.

    Tunable physics

    Over the past two years, researchers have experimented with different configurations of graphene and other materials to see whether twisting them at certain angles would bring out exotic physical behavior. Jarillo-Herrero’s group wondered whether the fascinating physics of magic-angle graphene would hold up if they expanded the structure, to offset not two, but four graphene layers.

    Since graphene’s discovery nearly 15 years ago, a huge amount of information has been revealed about its properties, not just as a single sheet, but also stacked and aligned in multiple layers — a configuration that is similar to what you find in graphite, or pencil lead.

    “Bilayer graphene — two layers at a 0-degree angle from each-other — is a system whose properties we understand well,” Jarillo-Herrero says. “Theoretical calculations have shown that in a bilayer-on-top-of-bilayer structure, the range of angles over which interesting physics would happen is larger. So this type of structure might be more forgiving in terms of making devices.”

    Partly inspired by this theoretical possibility, the researchers fabricated a new magic-angle structure, offsetting one graphene bilayer with another bilayer by 1.1 degrees. They then connected the new “double-layer” twisted structure to a battery, applied a voltage, and measured the current that flowed through the device as they placed the structure under various conditions, such as a magnetic field, and a perpendicular electric field.

    Just like magic-angle structures made from two layers of graphene, the new four-layered structure showed an exotic insulating behavior. But uniquely, the researchers were able to tune this insulating property up and down with an electric field — something that’s not possible with two-layered magic-angle graphene.

    “This system is highly tunable, meaning we have a lot of control, which will allow us to study things we cannot understand with monolayer magic-angle graphene,” Cao says.

    “It’s still very early in the field,” Jarillo-Herrero says. “For the moment, the physics community is still fascinated just by the phenomena of it. People fantasize about what type of devices we could make but realize it’s still too early and we have so much yet to learn about these systems.”

    This research was funded, in part, by the U.S. Department of Energy, the National Science Foundation, the Gordon and Betty Moore Foundation, and the Sagol Weizmann-MIT Bridge Program.

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    MIT Seal

    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

    MIT Campus

  • richardmitnick 11:45 am on May 4, 2020 Permalink | Reply
    Tags: "Study: Life might survive and thrive in a hydrogen world", Astronomers will be able to aim the new megascopes at nearby exoplanets., , , , , MIT   

    From MIT News- “Study: Life might survive, and thrive, in a hydrogen world” 

    MIT News

    From MIT News

    May 4, 2020
    Jennifer Chu

    New research suggests that next-generation telescopes might look first for hydrogen atmospheres, as hydrogen can be a viable, easily detectable biosignature of life. Image: NASA/JPL

    When searching for extraterrestrial life, astronomers may want to look at planets with hydrogen-rich atmospheres.

    As new and more powerful telescopes blink on in the next few years, astronomers will be able to aim the megascopes at nearby exoplanets, peering into their atmospheres to decipher their composition and to seek signs of extraterrestrial life. But imagine if, in our search, we did encounter alien organisms but failed to recognize them as actual life.

    That’s a prospect that astronomers like Sara Seager hope to avoid. Seager, the Class of 1941 Professor of Planetary Science, Physics, and Aeronautics and Astronautics at MIT, is looking beyond a “terra-centric” view of life and casting a wider net for what kinds of environments beyond our own might actually be habitable.

    In a paper published today in the journal Nature Astronomy, she and her colleagues have observed in laboratory studies that microbes can survive and thrive in atmospheres that are dominated by hydrogen — an environment that is vastly different from Earth’s nitrogen- and oxygen-rich atmosphere.

    Hydrogen is a much lighter gas than either nitrogen or oxygen, and an atmosphere rich with hydrogen would extend much farther out from a rocky planet. It could therefore be more easily spotted and studied by powerful telescopes, compared to planets with more compact, Earth-like atmospheres.

    Seager’s results show that simple forms of life might inhabit planets with hydrogen-rich atmospheres, suggesting that once next-generation telescopes such as NASA’s James Webb Space Telescope begin operation, astronomers might want to search first for hydrogen-dominated exoplanets for signs of life.

    “There’s a diversity of habitable worlds out there, and we have confirmed that Earth-based life can survive in hydrogen-rich atmospheres,” Seager says. “We should definitely add those kinds of planets to the menu of options when thinking of life on other worlds, and actually trying to find it.”

    Seager’s MIT co-authors on the paper are Jingcheng Huang, Janusz Petkowski, and Mihkel Pajusalu.

    Evolving atmosphere

    In the early Earth, billions of years ago, the atmosphere looked quite different from the air we breathe today. The infant planet had yet to host oxygen, and was composed of a soup of gases, including carbon dioxide, methane, and a very small fraction of hydrogen. Hydrogen gas lingered in the atmosphere for possibly billions of years, until what’s known as the Great Oxidation Event, and the gradual accumulation of oxygen.

    The small amount of hydrogen that remains today is consumed by certain ancient lines of microorganisms, including methanogens — organisms that live in extreme climates such as deep below ice, or within desert soil, and gobble up hydrogen, along with carbon dioxide, to produce methane.

    Scientists routinely study the activity of methanogens grown in lab conditions with 80 percent hydrogen. But there are very few studies that explore other microbes’ tolerance to hydrogen-rich environments.

    “We wanted to demonstrate that life survives and can grow in an hydrogen atmosphere,” Seager says.

    A hydrogen headspace

    The team took to the lab to study the viability of two types of microbes in an environment of 100 percent hydrogen. The organisms they chose were the bacteria Escherichia coli, a simple prokaryote, and yeast, a more complex eukaryote, that had not been studied in hydrogen-dominated environments.

    Both microbes are standard model organisms that scientists have long studied and characterized, which helped the researchers design their experiment and understand their results. What’s more, E.coli and yeast can survive with and without oxygen — a benefit for the researchers, as they could prepare their experiments with either organism in open air before transferring them to a hydrogen-rich environment.

    In their experiments, they separately grew cultures of yeast and E. coli, then injected the cultures with the microbes into separate bottles, filled with a “broth,” or nutrient-rich culture that the microbes could feed off. They then flushed out the oxygen-rich air in the bottles and filled the remaining “headspace” with a certain gas of interest, such as a gas of 100 percent hydrogen. They then placed the bottles in an incubator, where they were gently and continuously shaken to promote mixing between the microbes and nutrients.

    Every hour, a team member collected samples from each bottle and counted the live microbes. They continued to sample for up to 80 hours. Their results represented a classic growth curve: At the beginning of the trial, the microbes grew quickly in number, feeding off the nutrients and populating the culture. Eventually, the number of microbes leveled off. The population, still thriving, was stable, as new microbes continued to grow, replacing those that died off.

    Seager acknowledges that biologists do not find the results surprising. After all, hydrogen is an inert gas, and as such is not inherently toxic to organisms.

    “It’s not like we filled the headspace with a poison,” Seager says. “But seeing is believing, right? If no one’s ever studied them, especially eukaryotes, in a hydrogen-dominated environment, you would want to do the experiment to believe it.”

    She also makes clear that the experiment was not designed to show whether microbes can depend on hydrogen as an energy source. Rather, the point was more to demonstrate that a 100 percent hydrogen atmosphere would not harm or kill certain forms of life.

    “I don’t think it occurred to astronomers that there could be life in a hydrogen environment,” says Seager, who hopes the study will encourage cross-talk between astronomers and biologists, particularly as the search for habitable planets, and extraterrestrial life, ramps up.

    A hydrogen world

    Astronomers are not quite able to study the atmospheres of small, rocky exoplanets with the tools available today. The few, nearby rocky planets they have examined either lack an atmosphere or may simply be too small to detect with currently available telescopes. And while scientists have hypothesized that planets should harbor hydrogen-rich atmospheres, no working telescope has the resolution to spot them.

    But if next-generation observatories do pick out such hydrogen-dominated terrestrial worlds, Seager’s results show that there is a chance that life could thrive within.

    ESO/E-ELT, 39 meter telescope to be on top of Cerro Armazones in the Atacama Desert of northern Chile. located at the summit of the mountain at an altitude of 3,060 metres (10,040 ft).

    TMT-Thirty Meter Telescope, proposed and now approved for Mauna Kea, Hawaii, USA4,207 m (13,802 ft) above sea level, the only giant 30 meter class telescope for the Northern hemisphere


    Giant Magellan Telescope, 21 meters, to be at the Carnegie Institution for Science’s Las Campanas Observatory, to be built some 115 km (71 mi) north-northeast of La Serena, Chile, over 2,500 m (8,200 ft) high

    Vera C. Rubin Observatory Telescope currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    NASA/ESA/CSA Webb Telescope annotated


    As for what a rocky, hydrogen-rich planet would look like, she conjures up a comparison with Earth’s highest peak, Mt. Everest. Hikers attempting to hike to the summit run out of air, due to the fact that the density of all atmospheres drop off exponentially with height, and based on the dropping off distance for our nitrogen- and oxygen-dominated atmosphere. If a hiker were climbing Everest in an atmosphere dominated by hydrogen — a gas 14 times lighter than nitrogen — she would be able to climb 14 times higher before running out of air.

    “It’s kind of hard to get your head around, but that light gas just makes the atmosphere more expansive,” Seager explains. “And for telescopes, the bigger the atmosphere is compared to the backdrop of a planet’s star, the easier it is to detect.”

    If scientists ever get the chance to sample such a hydrogen-rich planet, Seager imagines they might discover a surface that is different, but not unrecognizable from our own.

    “We’re imagining if you drill down into the surface, it probably would have hydrogen-rich minerals rather than what we call oxidized ones, and also oceans, as we think all life needs liquid of some kind, and you could probably still see a blue sky,” Seager says. “We haven’t thought about the entire ecosystem. But it doesn’t necessarily have to be a different world.”

    Seed funding was provided the Templeton Foundation, and the research was, in part, funded by the MIT Professor Amar G. Bose Research Grant Program.

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    MIT Seal

    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

    MIT Campus

Compose new post
Next post/Next comment
Previous post/Previous comment
Show/Hide comments
Go to top
Go to login
Show/Hide help
shift + esc
%d bloggers like this: